PROJECT SUMMARY/ABSTRACT The number of U.S. adults treated annually for melanoma, the most deadly form of skin cancer, has nearly doubled in the past 15 years and the incidence rate is projected to again double by 2030. This growth is partly attributed to the popularity of artificial ultraviolet-emitting indoor tanning beds. Despite recognition by numerous national and international health organizations as being carcinogenic to humans, nearly 10 million Americans use indoor tanning beds each year. An estimated 1 in 10 of all new U.S. cases of melanoma and 400,000 annual cases of non-melanoma skin cancer are directly attributable to indoor tanning. Most concerning, nearly 1 in 5 young adult white females engage in high-risk indoor tanning, defined as using indoor tanning beds at least ten times a year, which is associated with a substantially increased risk of melanoma. As indoor tanning gained popularity among young women over the past two decades, melanoma has recently become one of the most common cancers among this population. The 2014 Surgeon General's Call to Action to Prevent Skin Cancer identified a critical research gap related to an absence of interventions that target high risk indoor tanners and address underlying motives for tanning, including ?the desire to look attractive and healthy and to conform to societal beauty standards?. The purpose of this application is to implement and test an intervention designed to encourage indoor tanning cessation among high-risk tanners. The intervention is unique in using persuasive techniques and content to reduce perceived pressure to be tan, reduce the value placed on tanning, and promote positive body image rather than focusing on information about the risks of tanning. The intervention will be delivered via the social media site Facebook through the ?secret groups? feature. The use of Facebook groups will allow group-based interactions among participants, which can facilitate stronger changes in attitudes and behaviors, and provides a platform to embed the intervention into individuals' normal routines. The first proposed aim is to refine the existing intervention content from our preliminary intervention studies with user-generated feedback. The second aim is to conduct a randomized controlled trial of the intervention in a sample of 400 young women engaged in high-risk tanning. Our primary hypothesis is that participants who receive the intervention will report less indoor tanning at a 6-month follow-up compared to those who participate in a control Facebook group. Our third aim will examine hypothesized psychosocial mediators of the intervention effects. The intervention has strong potential for cost-effective, widespread dissemination and targets a group at high-risk for future cancer development. If effective, the intervention has the potential to significantly reduce the growing burden of melanoma and other skin cancers.